The use of behaviour modification techniques in educational settings is growing steadily in this country. (Ward, 1971; Atkinson, 1975; Tsoi and Yule, 1976; and Brown, 1977). Many teachers are being attracted to these techniques because of the logical approach, the verified principles from which they are derived, the possibility of objective evaluation, the general interest of children in their use and—importantly—the fact that techniques are only a more systemised version of teaching children than they have been using themselves for decades. Clarizio and Yelon (1967) have given several reasons why teachers are appropriate people to use behaviour modification. They note that behaviour modification focuses on behaviour as it presents, rather than on its causes which helps the teacher as he is not normally trained to probe for such causes, is rarely in a position to directly manipulate the cause to effect change and probably knows from experience that even when causes have been isolated and manipulated by other professionals, the behaviour may still persist in the classroom. Unfortunately in some descriptions of the use of behaviour modification not enough thought is given to distinguishing for the reader what are the essentials for experimental design and what are the essentials for a practising teacher in the classroom.